1. Field of the Invention
The invention relates to highly wear resistant and durable bearing shells for connecting rods as well as suitable fabrication processes.
The usual procedure for the fabrication of bearing shells of this type is to line a base material (e.g. steel or light metal) with a pre-fabricated bearing shell.
With the development of new generations of motor vehicles the requirements on the materials used in the engine are constantly increasing. The available bearings of the engines, and the connecting rod bearings in particular, are no match for the resulting increasingly high mechanical loads, especially on the long term.
While in the past Pb-containing alloys on Cu-basis have frequently been used as slide bearing material, they are today increasingly replaced by Pb-free alloys for environmental reasons.
For cost considerations it is not desirable to fabricate the bearing shells as individual pieces and to fit them into and connect them with the connecting rod, but rather, it is preferred to directly deposit the bearing shell as a coating onto the surface of the connecting rod eye.
2. Description of Related Art
In DE 197 31 625 processes are disclosed which deposit the bearing layer directly by means of thermal spraying of a bearing material onto the connecting rod eye.
Often the bearing layers feature an additional sliding layer on their surface made from a comparable soft material. This is made using e.g. Pb-alloys or Al/Sn-alloys. As slide bearings for higher technical requirements Al/Cu-alloys are known with Sn-contents in the range of 17 to 35% by weight. WO 9100375 describes a bearing with a contact layer which is made from a base material, in particular Al, and a dispersed phase therein, in particular Sn. The sliding layer is deposited by a sputtering process.
With respect to high mechanical loads which especially result in high temperatures in the sliding zone the known sliding layers do not exhibit the required long term stability and under dry running conditions do not provide the required safety margin regarding galling. Especially with the demanding requirements of modern engines a partial short term outage of the oil cooling on the sliding surface is not a rare operating condition, resulting in very demanding requirements with regard to the dry running ability.